Vacuum pump



y 2, 9 "K. c. D. HICKMAN 2,206,093

VACUUM PUIP Filed Jan. 4, 1939 Patented July 2, 1940 UNITED STATES 2,200,523 vacuum rm Kenneth C. D. Hickman, Rochester, N. 12, as-

signer to Distillation Products, Inc., Rochester, N. Y., a corporation of Delaware Application January 4, ma, Serial No. 249,210

This invention relates to improved methods stituents to the jet operating in the high presin sequence through a series of boilers supplying vapors to the series of jets. The high vapor pressure constituents are vaporized in the boilers supplying vapors to the Jets operating at the high pressure end of. the pump. Unvolatilized 2 components of the pump fluid then pass in sequence through the various boilers and finally.

the lowest vapor pressure constituents are vaporized and supplied to the boiler supplying vapors to the Jets at the low pressureend of the pump. Since these pumps were described by me to the public they have been extensively used and various modifications have been devised. The principles upon which the pump operates are therefore well known and need not be further described.

This invention has for its object to improve the degree of vacuum and/or the rate of vacuum production obtainable by means of fractionating condensation pumps. Other objects will appear hereinafter.

These and other objects are acomplished' in accordance with my invention which includes means for withdrawing pump fluid from one of the boilers toward the low pressure end of the pump and circulating it over a surface or surfaces in contact with gases or vapors present in the low pressure end of the pump.

During the operation of the kind of vacuum pump employing a vapor stream, the low pressure side of the pump becomes fllled with a gas composed of pump oil molecules. This gas exerts the saturation pressure of the liquid pump fluid at the temperature existing inthis part of the pump. The saturation pressure of the best pump fluids in a suitable fractionating pump may be extremely low, for instance, 10- mm. of mercury at 20 C. While such a pressure is amply low enough for most academic or industrial operations, nevertheless a saturated vapor at this pressure can, over. long periods of time,

deposit a film of pump fluid on the walls and parts of the vessel that is being evacuated. Difficulties with poorer types of pump fluids would. be much greater. 1

It is well known that the saturation pressure can be reduced by placing between the apparatus and the pump a cold trap'or sink. I have found that the saturation pressure can be eflectively reduced by circulating those constituents of the pump fluid, which have failed to evaporate during heating in the pump, over the low pressure zones or the intake side of the pump.. During its circulation this liquid absorbs parts of the gases and vapors, and reduces their pressure below the saturation point at the prevailing temm perature.

In order to clearly illustrate the operation of my invention, I have shown in the accompanying drawing two of the preferred embodiments thereof wherein: 2

Fig. 1 is a vertical section of a vertical condensation pump constructed of a plurality of concentric tubes, the base of which form a plurality of boiler compartments and the upper ends of which terminate in pumping jets; 25 Fig. 2 is a vertical section of a preferred form of horizontal pump; and

Fig. 3 is a horizontal section'taken on line 3-3 of Fig. 2.

Referring to Fig. l, numeral 2 designates a so tubular outer casing provided with a flange ,l at the top thereof which is to assist in connecting to the receptacle which is to be evacuated. Numeral 0 de gnates a plate which-serves to close the base of the tube 2 and is integral therewith. 5 Numeral I designates a heating unit within which isdisposed resistance heating wires l0. Toward the lower end of the casing 2 is an integral conduit I: which serves to connect the high" pressure end of the. pump to a backing pump (not 4 shown). Numerals l4, l8 and I8 designate concentric tubes, the base of each of which rests in close contact with base plate 6. Numerals 20, '22, and 24, designate annular shaped elements which close the top end of each tubular element I4, I! and II, respectively, and which cooperate therewith to form Jet nozzles 26, 28, and 30. A plurality( of holes 12, 34 and 3! permit the flow of vapors from inside of each tubular element into the respective iet nomles. The base of each 50 tubular element l4, l6 and I8 is provided with a series of small holes 38, 40 and 42 which are of restricted areas. Numeral l4 designates a collar integral with tubular element II which extends into close proximity with walls of casg3 ing 2. Numeral 4t designates a conduit which terminates near the center of the central tubular element ll and which serves to withdraw fluid therefrom and convey it into pump 48 which, in

turn, serves to pump the fluid through cooler ll, conduit l2 and into the distributing head ll. Numeral Ii designates a plurality of superimposed annular-disks so constructed that they will shed fluid from one to the next lowest disk by gravity, much in the same way that shingles on a roof, shed rainwater. Numeral l0 designates the flrst such element upon which the pump fluid flrst flows as it falls from the distributing head I4. II" designates the last disk or the series, the lower edge of which is in close proximity to the inner wall of casing 2.

Referring to Figs. 2 nates a cylindrical pump casing which is adapted to be connected at the low pressure end by flange 22 to the chamber to be exhausted, and at the high pressure end by conduit 84 to a backing pump (not shown). II is closed by a plate I! integral with conduit ll. The base of cylinder II in the vicinity of the high pressure end is cut away and the extended walls I! and I1, closed by a base plate ll so as to form a recessed pump fluid boiler. A similarly shaped cylinder ll is located .within the main casing- II and more or less concentric therewith. The portion of this cylinder adjacent the high pressure end of the pump is cut away and provided with an extension corresponding to that of the pump liquid boiler. The end of the cylinder .0 is closed by a plate 92 which is integral with a conduit II which extends slightly into conduit 84 as illustrated. Plate. 22 extends to the base plate ll of the boiler. A similarly shaped plate M located inside the cylinder ll extends from the top inside wall oi the cylinder to the base plate ll. Plate It is similarly shaped and likewise extends to the base plate ll. Plate 28 is integral with the lower wail of cylinder II and extends to the base plate 8| 0! the boiler.v

Two bent plates Ill and "2 integral with the lower wall oi. the cylinder OI, extend transversely to plates 92, ll, .8 and I and are integral therewith. They serve to segregate the pump liquid boiler into a plurality of compartments, A, B, and C. Cylinder ll is trlmcated at 98 and the truncated portion is extended to, and becomes integral with conduit I. Jet nozzle I" is mounted at the high vacuum end oi! conduit Ill. Jet nozzle I is similarly located at the end oi cylinder ll. Holes I" and Ill provide a passageway for working vapors to issue into jets I" and Ill respectively.

Numeral H4 designates a semi-circular opening in the base of plate 9!. It is sufliciently small that it is well covered by pump fluid. These openings are two in number. Numerals Hi, H9 and I2! designate similar openings in the base of plates 82, 94 and SI respectively. Numeral ll! designates a conduit which extends along.

the base of the boiler through openings in the various partition plates. These openings are preferably small so that a tight flt results. Conduit II! is bent upward at H! and terminates at the bottom central portion of the casing II. The other end of the conduit terminates at the low pressure end of the boiler.

Numeral I 2| designates a series of fractionating rings integral with the wall of conduit 84. Conduit I23 connects the space between the last two rings l2l with the low pressure portion of the boiler. Numeral I22 designates a cooling and 3, numeral 8| deslg The high pressure end of coil integral with the external wall of the pump casing. Cooling fluid is introduced at I24 and withdrawn at I20. Numeral l2! designates a sight-glass whereby the level of the pump fluid can be readily determined.

Numeral I 3| designates a pump connected to the sight-glass I28 which is in turn connected to a conduit I82 which terminates in a distributing device Ill located at the top 0!, pump casing ll. Distributing device I is provided with a plurality of small holes lli which project in an upward direction. Numerals I38, I40 and I42 designate a plurality of baflles, located in the intake end or low pressure end or the pump. Numeral I designates a hole at the base of Me III.

In operation employing the apparatus illustrated in Pig. 1, pump fluid, such as di-Z-ethyl hexyl phthalate is introduced into the pump to a height sufllcient to cover the tops of openings "-42. A height half way between collar 44 and base i would be sumcient. Flange 4 is connected to the system to be evacuated and conduit i2 is connected to the backing pump which is put into operation. Heating element 8 is then started. Pump fluid is vaporized at the base 01' tubular element it and the vapors rise, pass through openings ll, Jet 30 and are condensed on the walls of easing 2. down the walls between casing wall 2 and collar 44 and thence into the boiler enclosed by tubular element It. Here the high vapor pressure constituents are vaporized, pass through openings 32 and out through jet 26. Condensate accumulating upon the walls of casing 2 flows back into the boiler past collar 44 and through openings ll.

Pump fluid not vaporized in the boiler of tubular element ll flows through openings 40 into the boiler oi tubular element It. Here the next vapor pressure constituents are vaporized and the vapors passed through openings 34, through Jet 28 and are condensed on the walls and returned to the boiler as described previously. It is seen that pump fluid which is vaporized in the boiler at the base oi. tubular element It is that which was not vaporized in the other two boiler compartments and which, therefore, is the lowest vapor pressure component of the pump fluid. During the pumping action secondary pump 48 is put into operation and this low vapor pressure pump fluid in the boiler I8 is withdrawn through conduit 46, circulated through cooler 50 and conduit 52 and finally introduced onto the top 01' flange it. The fluid i'ollows over the series 01' flanges 56 until it reaches the lowest flange 50" from which it flows onto the inner surface of casing 2. It-then flows by gravity down to'the boiler at the base of the pump where it goes through the iractionating operation previously described. 4

Pump 4! should be run at a speed sufllcient to keep a thin fllm of liquid on the flanges 56. However, it should not be run so fast that the supply of fluid in the boiler at the base of tubular element II is depleted. In other words, a body oi fluid should always be retained in this boiler.

Gases entering the top casing 2 pass through the spaces between flanges 56. However, in doing so they sufl'er at least one collision therewith. Various gases and vapors are thus absorbed in the liquid fllm which is then delivered to the low pressure end of the pump. The absorbed gases and vapors are driven 01! in the boiler at the base of tubular element It and pass out throug' The condensate flows compartments A, B and C.

let 2| and are eventually removed by the backing pump connected to conduit I2.

In operating the apparatus illustrated in Figs; 2' and 3, pump fluid'is introduced into the boiler The pump fluid is indicated at I25 and is shown as it would be retained by the. boiler during operation of the pump. It will be noted that the'pump casing 80 and the base of the boiler 88 slant upwardly toward the high vacuum end. This is to cause the pump liquid toflow back into the boiler compartments. Flange I2 is connected to the chamber to be evacuated and conduit N is connected to any suitable backing pump. The boiler containing the pump fluid is heated in any suitable manner, such as by gas. The lowest vapor pressure pump fluid constituents vaporize and pass into compartment A and thence through jet nozzle 93. The jet of vapors passes into conduit M where it is condensed and entrained gases removed by the backing pump connected thereto. The condensed pump liquid flows back over fractionating rings Iii and is returned to the boiler by conduit I23. High vapor pressure constituents having no utility are retained by the fractionating rings iii and may be intermittently removedi therefrom by a suitably located conduit.

Components which are not vaporized in section A flow into B. Although compartment B is at a higher elevation than compartment A, compartment A is at .a somewhat higher pressure so that the pump fluid is caused to flow more or less uphill into compartment B. In compart-- ment B the intermediate fraction representing the most useful components of the pump fluid is vaporized and passes into conduit III and thence to jet I06. Vapors from this jet condense on the cooled walls of 80 and flow to the base and into conduit H5. They then flow through conduit H5 to the lowest portion of the boiler as indicated at I21. The lowest vapor pressure constituents are not vaporized in compartment-B, but flow into compartment C. Here the low J vapor pressure, decomposable substances are vaporized and issue through the intermediate jet I08. Vapors from this jet condense on the walls of casing III and flow by gravity back into condgit III and eventually return to compartment I I.

Pump fluid accumulating in section I2! and sight-glass I2! is pumped by pump I through conduit I32 into distributing device I" from which the pump fluid is ejected in a plurality of small'streams against the inside wall of casing 80. This pump fluid flows down the walls of the casing in a thin film and thence flows through opening I at the base of baiiie I3! along the bottom of casing 80 and into conduit III and II! by which it isdelivered to the boiler at the high pressure end of the pump. Gases being pumped and which diffuse into theintake end of the pump are caused to pass into contact with the film of liquid on the inside of casing l0 0 by baiiies I38, IIII and I42. Volatiles and gases are thus taken up and are conveyed by the pump fluid to the high pressure end of the pump where they are boiled oil and removed by the backing "pumpv The pump fluid which is circulated to the low pressure end of the pump and over-the baiiies may be taken from any of the lower vapor pressure boilers. It is obvious that the lowest vapor pressure components are the best for circulation since they will not give off volatiles or will give of! less volatiles than other components. Pump fluid from the boiler supplying vapor to the lowest pressure jet is usually to be preferred. Heavy residues from the pump or boiler in which they are accumulated are also very useful. In order to have a circulation liquid of very low vapor pressure accumulate in thelow pressure boiler or in the pump for the low volatiles it is in some cases advantageous to add to the pump fluid a very low vapor pressure component fol. this particular purpose. Examples of such particularly low vapor pressure substances which could be added to the ordinary pumping fluids are purified castor oil, di-ethyl phenyl phthalate and nonyl selacate and the like. When sucli substances are withdrawn and circulated over the baii'ies they have the advantage that they have flower. vapor pressure than any of the components issuing from the jets. Therefore they are able to quite effectively absorb vapors of the latter when they difluse back into contact with the baiiies..

Various modifications can be made in the apparatus described without departing from the spirit or scope of my invention. For instance, it would be desirable to prevent exposure of the circulated liquid to the'action of the hot vapors issuing from the various jets since this might possibly drive oi'i some volatiles. This/could be avoided by collecting the circulated liquid after it has adbsorbed gases andvapors in a closed conduit and directly conveying it to a boiler at or near the high pressure end of the pump. Al though I have illustrated conveying the circulated liquid containing absorbed gases to the' boiler at the high pressure end of the pump, it could be circulated to an intermediate boiler without losing the advantages of my invention.

sults to a slight extent and is not preferred, 4

however, it will give substantially better results than if no circulating expedient is employed and is contemplated as being part of my invention. It is preferable to cool the circulated liquid as' illustrated in Fig. 1. This materially reduces the vapors present to well below the saturation point so that there is little chance of their precipitating or condensing. Warm circulating liquid or the intermediate fractions may be .used since they have the necessary efl'ect of reducing the saturation pressure although not as emciently as the lower vapor pressure fractions and lower temperatures.

This application is a continuation in part of my U. 8. Patent #2,153,189, April 4, 1939.

I claim:

1. A condensation pump adapted to employ an organic working fluid, characterized by means,

located at the high vacuum end, or intake side the boiler containing lower vapor pressure constituents and circulating it into contact with gases or vapors entering the lower pressure side of the pump.

8. A multi-stage fractionating condensation pump adapted to employ a mixed organic liquid as a pumping fluid and in operation to segregate the components thereof so that the low vapor pressure components exert their pumping action toward the low pressure side and the high vapor pressure components toward the high pressure side of the pump. characterized by means for circulating a low vapor pressure constituent of the pump fluid segregated in the pump over the interior of the intake end of the pump.

4. A multi-stage fractionating condensation pump adapted to employ a mixed organic pumping fluid and in operation to segregate the components thereof in a plurality of boilers so that the low vapor pressure components exert their pumping action toward the low pressure side and the high pressure components toward the high pressure side of the pump, characterized by means, connected to a boiler containing the lowest vapor pressure components for withdrawing pump fluid therefrom and circulating it over a surface located in the low pressure or intake end of the pump.

5. A multi-stage fractionating condensation pump adapted to employ a mixed organic pumping fluid and in operation to segregrate the components thereof in a plurality of boilers so that the low vapor pressure components are vaporized in the boiler or boilers supplying working vapors to the low pressure side of the pump and the high vapor pressure components are vaporized in the boiler or boilers supplying working vapors to the high pressure side of the pump characterized by means connected to a boiler supplying vapors to the low pressure side of the pump for withdrawing pump fluid therefrom and circulating it in a thin i'ilm over a relatively large surface exposed to gases or vapors entering the pump and means for collecting the circulated fluid and conveying it to a boiler at the high pressure end of the pump.

6. A multi-stage fractionating condensation pump adapted to employ a mixed organic pumping fluid and in operation to segregate the components thereof in a plurality of boilers so that the low vapor pressure components are vaporized in the boiler or boilers supplying working vapors to the low pressure side of the pump and the high vapor pressure components are vaporized in the boiler or boilers supplying working vapors to the high pressure side of the pump characterized by means connected to a boiler containing low vapor pressure components for withdrawing pump fluid therefrom and circulating it over a surface located in the intake end of the pump.

7. A multi-stage fractionating condensation pump adapted to employ a mixed organic pumping fluid and in operation to segregate the components thereof in a plurality of boilers so that the low vapor pressure components are vaporized in the boiler or boilers supplying working vapors to the low pressure side of the pump and the high vapor pressure components are vaporized in the boiler or boilers supplying working vapors to the high pressure side of the pump characterized by a secondary pump the intake side of which is connected to the boiler which contains the lowest vapor pressure components and the discharge side of which is connected to a distributing or spreading device located in the low pressure end of the condensation pump, and means for collecting the thus circulated liquid and conveying it to a boiler located at the high pressure side of.

the pump.

8. A multi-stage fractionating condensation pump adapted to employ a mixed organic liquid as a pumping fluid and in operation to segregate the components thereof so that the low vapor pressure components exert their pumping action toward the low pressure side and the high vapor pressure components toward the high pressure side of the pump, characterized by means for cooling and circulating a low vapor pressure constituent of the pump fluid segregated in the pump, over the interior of the intake end of the pump.

9. A multi-stage fractionating condensation pump adapted to employ a mixed organic pumping fluid and in operation to segregate the components thereof in a plurality of boilers so that the low vapor pressure components exert their pumping action toward the low pressure side and the high vapor pressure components toward the high pressure side of the pump, characterized by means, connected to a boiler containing the lowest vapor pressure components for withdrawing pump fluid therefrom, cooling means for the withdrawn liquid and means for circulating the cooled liquid over a surface located in the low pressure or intake end of the pump.

10. A multi-stage fractionating condensation pump adapted to employ a mixed-organic pumping fluid and in operation to segregate the components thereof in a pluralityof boilers so that the vapor pressure components are vaporized in the boiler or boilers supplying working vapors to the low pressure side of the pump and the high vapor pressure components are vaporized in the boiler or boilers supplying working vapors to the high pressure side of the pump characterized by means connected to a boiler supplying vapors to the low pressure side of the pump for withdrawing pump fluid therefrom, means for cooling this liquid, means for circulating it in a thin film over a relatively large surface exposed to gases or vapors entering the pump and means for collecting the circulated fluid and conveying it to a boiler at the high pressure end of the pump.

KENNETH C. D. HICKMAN. 

